Rejuvenation of abrasive surfaces



was

3,177,627 REJUVENATEON F ABRASIVE SURFACES Martin M. Guihert, Port Orchard, and Curtis S. Skinner, Jr., Renton, Wash, assignors to The Boeing Company, Seattle, Wash, a corporation of Delaware Filed Aug. 3, 1962, Ser. No. 214,551

Claims. (Cl. 51262) This invention concerns grinding procedures, in general, and more particularly affords increased efiiciency in a number of respects in the grinding of a readily oxidizable metal with an abrasive element such as a grinder disk or sander belt. The increased efliciency is demonstrated by an increased rate of rem-oval of metal from a workpiece, by a much longer useful life of the abrasive element, by avoidance of down-time for rejuvenation or replacement of the abrasive element, and by the resultant lowering of grinding costs. 7

The invention, although usable when grindingaferrous metals, demonstrates its advantages most strikingly in the grinding of readily oxidizable metals, particularly aluminum and its alloys. Because its advantages are especially necessary when the workpiece is of a material the groundoff metal particles of which are readily oxidizable, it would also be highly advantageous in grinding magnesium, or any other metal or alloy which oxidizes at low temperatures, such as are developed at the point of grinding.

- Abrasive elements employed in such operations, whether abrasive coated disks or belts, or wheels in which abrasive particles are embedded, tend to become loaded with dust in the form of oxidized metal removed from the ground surface, mixed with metallic particles, which gradually decreases its efficiency, lessening the quantity that can be removed by grinding in a given period of time, involving periodical shut-downs for rejuvenation of the abrasive surface, or its replacement, lessening the over-all useful life of the abrasive surface, and increasing the cost of removing the required amount of metal. Grinding operations such as this are often used in the finishing of wing skins for aircraft, and in like operations, and the decrease in efliciency in the grinding operation increases materially the cost of such an airplane, particularly when aluminum alloys or the like are used.

It is the object of this invention to provide a method and apparatus for use in the work and under the conditions outlined, which will prolong the useful life of the abrasive "elements far beyond that heretofore expected or attained, largely eliminate shut-downs, increase by several times the amount of metal that can be removed in a given period of time, increase by one hundred or more times the 'total amount a given tool can remove during its useful life, all by enabling or effecting periodical removal of the oxidedust and rejuvenation of the abrasive surface without interruption of the grinding operation.

Also, it is an object to provide apparatus automatically operable through successive time sequences, related to the size of the abrasive particles used, and other factors, to

effect rejuvenation of the abrasive element.

The drawing is a diagrammatic showing of a typical machine useful in carrying out the process automatically;

United States Patent 0 3,177,627 Patented Apr. 13, 1965 that surface that the rate of metal removal from the workpiece drops, and other factors having to do with the efficiency of the operation are adversely affected. The procedure heretofore, at this stage, has been to use a solvent to flush out the particles, or an air blast to blow them away, to apply a vacuum to the abrasive surface, or to apply abrasive sharpening tools. Such procedures have proven so ineifective as to be commercially impractical, until the use of a particular type of oxidizer followed by and in combination with an air blast, as set forth in detail hereinafter, was hit upon.

The type of abrasive element employed, whether disk or belt, and the particle size of the abradant, are largely immaterial. Coated abrasive elements, such as a sander belt or disk, have been cleaned very successfully (the belt type is preferred, because of its uniform speed), yet the process works well with a grinder wheel in which abradant particles are embedded. The particle size is important only in the respect that finer particles tend to require rejuvvenation at shorter intervals than coarser particles,

although pressure would have some effect on this factor.

In essence, according to this invention, rejuvenation of the abrasive element is accomplished by applying to the element a type of lubricantwhich effects or facilitates oxidation and/or sulfurization or other chemical conversion of the metal particles to the oxide or other compound, of a nature which then collects as a dry dust upon the abrasive surface, and periodically blowing this dust from the surface by a blast of high velocity air, or'the like, before it clogs the spaces between particles. The pre-,

ferred procedure is to continue grinding without interruption, but at intervals first to blow the dust from the abrasive surface, and after cessation of the air blast to apply a small metered amount of an oil lubricant of a particular nature to the abrasive surface over a short period of time. The period of a cycle will vary with factors such as the abradant particle size, and the like, but with a vertical platen grinder belt using 36-grit particles, running at 3690 feet per minute, the time cycle required approximately ten minutes over all. Of this time the air blast, at p.s.i., was operative (the grinding continuing uninterrupted) for 30 seconds, the oil spray at 20 psi. in the form of a heavy spray began after say 10 seconds, and lasted 5 to 7 seconds, after which grinding continued for the remainder of a l0-minute cycle, before initiation of the next cycle. These figures are to be understood as illustrative and not restrictive.

The preferred arrangement is to use a relatively high pressure air blast, as indicated above, directed at some 45 counter to the direction of the sander belt, and quite close-say, only A; inch distant-40 the abrasive surface; the oil spray should be directed perpendicularly to the abrasive surface, from a distance of say 1 /2 to 2 inches. Maximum air pressure at the air nozzle-is important. A heavy oil spray, rather than a fine mist or fog, is preferred at the oil nozzle. The most suitable cycle time, in relation to linear inches of abrasive surface (other factors being equal) is one minute to each ten linear inches of abrasive surface; for example, 100 inches of belt length or wheel periphery should enable a tenminute cycle.

The oil lubricant found most suitable is a mineral-based oil product produced by Stuart Oil Co., of Chicago, Illinois and sold under the name Excelence NF. Other oils work with only slightly less efficiency. Such oils are, for example, Mobil-Met 29 and 27, and Anacut, each diluted with kerosene in the ratio of five parts of kerosene to one part of the oil, to a viscosity of SAE 3 or 4. The characteristic which is common to these oils is their ability to chemically oxidize and/or sulfurize more completely the metals (such as the aluminum or the magnesium mentioned) which are readily oxidizable at the temperatures prevalent at the point of grinding. Thereby particles ree es? m'ovedbyabrasion are converted 'to-fdust in the form of perature prevalent at the point of abrasion. V r

Thefine dust particles so produced'do not tend to agglonrerate nor weld.- ,Many drop from the abrasivesura face, and'fsuch as: collectjthere'. in time arebut' loosely adheredf Upon the application ofa highvelocity air blast; j

atsay 3700 feet'per minute, and under apress'ure of 1 j()0 ceedingapplication-of; the oil lubricant-coats the abrasive, surface with a fresh supply of the oxidation-facilitating product, using: the latterterm well as oxidation It is preferredthat any given cycle be constant in time ,7 succession and duration, to "which'end ia' typical automatic; machine; shown in 'the drawing-hasbeendevised; xThisf, includes the yertically,movingzsander belt 1, driven by a motorz at the optimum rate of speed,and a table 3'whereon the workpiece mayrest while'litengages the abrasive": element 1;: Ai1- frorn'any:convenient pressure-source is deliveredcby wayof duct 41th; a nozzle-,5, directed towards the-abrasive;element 1 at anKangle" of 45 7 counter to ,its'

,movement: Themetered oil'lubricant,is'delivered' as a 7 heavy spray; at-ZO p.s.i;', from, a'sreservoirfi, asbyapump; 7 by 'wa yof" duct" 8' tosa; noi zle 9', directed towards: the

' abrasive-element.

to includ'e sulfurization asfl the oxide, primarily, and perhaps-to a sulfate, at the-temproduced a number ofl advantages over the old method.

ltpermitted elimination of step No. 2, with a saving of. 'fourman hours-perZlOsquarefeet of aluminum alloy wingskin. The use of ExceleneNFfoil, which is the preferred' liquid applied, required only one pint for finishing 200. square feet, as against'one gallon of the solvent previously used, and ith'e Excelene NF cost fifteen cents less per gallon, resulting'jin a 'saving in'costlofe approximately- '9()%'.- Theain'ountfo'f, metal remov'ed infa given time was increased by atj-leastf four times,,over the "amount removed in the same period ofitime by dry' grinding, and in one test 29.9 poundswas removed by the method of this invention, as against 0.59fpounds by'dry; grinding.

' The usefullife of-the abrasive element-was extended by at a ofaniabrasive' belt hadbeenreduced by only an estimated p j 5%. In addition-economies resultedtrom'avoidance of f a a a WOIIi- 'Oll t barasive element c We'claimj as our invention:

7 Timing:- means are provided1 f0'r1 'eifecting' sequential dischargei of; air and" oillubricant," at regular intervals;

and a like valve- 11' in the: oil' duct 8, are biased to close,

but-are-opened atproper'intervals and for desired, periods,

by; a: suitabletiming device; s'uch 'as, th'ecams', 12 andy13.

GanrlZ closes switch 1:4'to" hold 'open'air valve '10 forfthe necessary period of time,-and at -the required inter-val,- and cam-r13; afterfclosureiot air, valve 10,-, closes switch 15V "to hold'open oil-valve 11' for the necessary short period; of

time; Thetwo cams12 and1-3 are conveniently'mounted In one'test its Was found that after 19 hoursrand-l9 minutes of grinding-by the process of'thisinevntion, the useful life shut-downs; and of time spent in removing and replacing fbltgin'thegrinding of a 'workpiece that is primarily of aluminum, whichv method comprises applying angox-ida tion-assisting oil' as a sprayto the abrasive surface of the tool,followingjthe application'to that surface of anair if blast to remove ground-off andoxidized particles;

:' ZLTh'e'method of cIaim Llin which application'of the, air blast occurs after an; interval in excess of nine min;

utes from the preceding oil application, and lastsfor approximately; thirty seconds, and is followed after'an Q interval;ofapproximately ten seconds by application of the oil spray-during approximately; five seconds; V '1 3. "Mechanism for useinj the grindingof metal'wo'rle pieces, to extend the useful life zof. the abrasive tool emupon'thewsameshaft, an'dcan be, driven from the synchro nous 'motor 16, through the speed re'ducing gear at 17 Thereby thetiming of the air blast at .nozzle' 5 and' of the oil s'prayidi'schar'ge at 9, is. controlled; and the length or; a

cycle' determi'ned, eitheras: giveninthe example above,

or otherwisewas maybefonnd necessary;

Timing means, and; control jmechanism,

the amount especiallyfof the oil, discharged at the' no'zzles,

of any other'suitable typelmaybe used l Assuming-the abrasive element 1- to be employed in;

grinding-material frorn-a'workpiece of the nature specified; which is supported at 3,;after; aperiod-of time that varies with the pressure; the speed 'of the abrasive element; the

- coarseness of its'grit, the lengthg ofthe belt,;and' similar i I factors, the abrasive;- element collects adust :which' is 'prin marily the oxideof the'metalof which the workpiece is;

made. I Theair blastat 5 begins, andblows this dus'tfrom the abrasive element 1.5, Thereafterthe; oil-lubricant is dis-: charged at 9 onto 1 theabrasivej element, now largely clearr :1

of =thepotentially clogging-dust. Thisyoil has thelpropertyi-f I for regulatin f ployed, which comprises, in combination) with s'uch an abrasive" tool, "an :oil-spray'nozzle located, for dischargeof' an' oil lubricant uponthe' abrasive"surface of the a tool, an 'air' blast nozzle, also located for discharge of air onto the abrasivesurface, and-means. operable after T ,is a unidirectional-sander belt: a, 7 t 5'. Mechanism as in -claim 3, including means automatically operable atgthe initiationfofr" each blast, to

of chemically facilitatingthej conversion of the ground-elf I metal particles into the dust-:like'oxide, using the latter term'- in* the broad; sense, as "indicated above.-. ]So much thereof as does notr drop off colleetsslo'wly; and is again blown offbefore the grinding efliciency is too greatly re- 7 p of its, optimurrn; This process is-rePeated" at regulatintervals;automatically,

. a p v Heretofore the normal wing skin grinding: operation in production included the steps of: (1) finishing and blend ing dry with ajdisc grinder, (2) finishing dry with a doubleheaded vibratorysandeg; and 3(3) vibratory finishing wet, withr-a solvent; i Ithasheen' found by testsunder-produc tion conditions that the use "ofthe' method of this invention 9 a predeterminediperiod'ofgrinding to eflect for limited- I times discha'rgelof air followed by discharge of oil at g p a the respective nozjzles.

a I 4Q Mechanism as in claim 3, wherein*the abrasive tool effect discharge of air'tr'om the rair *nozzlefor a; pre

determined :vperiod, and discharge of thejoilfor a pre determined period t'r'ornjthe 'oil nozzle,'following cessation 1 of the air blast. p p, I

ReferencesCitedhyithExaminer V V UNITED srA r'Es r ParnNrs 1,637,487"

: LESTER Exam ine'r. l

' JOHN/C. CHRISIIE, FRANK Hi. BRQNAUGH, 3 5

Examiners,v

least three times-this alone reducing their cost by i V 1; Themetlmddf increasing the 'efiiciency and extend-- 7 ring the us'efullifeyof anabrasive tool such as a sander; 

3. MECHANISM FOR USE IN THE GRINDING OF METAL WORKPIECES, TO EXTEND THE USEFUL LIFE OF THE ABRASIVE TOOL EMPLOYED, WHICH COMPRISES, IN COMBINATION WITH SUCH AN ABRASIVE TOOL, AN OIL SPRAY NOZZLE LOCATED FOR DISCHARGE OF AN OIL LUBRICANT UPON THE ABRASIVE SURFACE OF THE TOOL, AN AIR BLAST NOZZLE ALSO LOCATED FOR DISCHARGE OF AIR ONTO THE ABRASIVE SURFACE, AND MEANS OPERABLE AFTER A PREDETERMINED PERIOD OF GRINDING TO EFFECT FOR LIMITED TIMES DISCHARGE OF AIR FOLLOWED BY DISCHARGE OF OIL AT THE RESPECTIVE NOZZLES. 